Blends of isotactic polypropylene with amorphous ethylene/propylene copolymers (EPM) or with ethylene/propylene/diene terpolymers (EPDM) are well known. The EPDM is crosslinked through the diene unsaturation to provide products having good toughness and chemical resistance characteristics. Overall, certain of these blends based on crosslinked EPDM have a good balance of mechanical and chemical properties, which give these products utility in wire and cable, hose, and gasket applications. It has been proposed to substitute amorphous EPM for EPDM because EPM is less expensive; however, attempts to crosslink the EPM with an organic peroxide in the presence of the isotactic polypropylene lead to chain scission of the polypropylene and to the production of thermoplastic olefins with inferior properties.